Steam-turbine.



C. E. SEARCH & I. W. MOORE.

STEAMTURBINE. APPLICATION FILED AUG'. I3. |913. RENEWED SEPT.2.' 1915.

Patented J une 13, 1916.

f .l i l liti @HABILES EDWIN' SEARCH AND JOSEH yW. MORE, OF MILWAUKEE,WISCONSIN, ASSIGNOBS T0 ALLIS-CHALMERS MANUAQTURXNG COMPANY, 0FMILWAUKEE,

WISCONSIN, A CORPORATION 0F DELAWARE.

' STEAM-TUINE;

ademas.

Application le August 13, 1913, Serial No. 784,779. Renewed. September20, 1915. Serial No. 52,113.

To all 'whom t may concern Be it known that we, CHARLES EDWIN SEARCH andJOSEPH .W. MOORE, citizens of the United States, residing at Milwaukeeand West- Allis, Milwaukee, respectively, .1n the county of Milwaukeeand State of Wisconsin, have invented a certain new and use; fulimprovement in Steam-Turblnes, of which the following is aspecification.

This invention relates to improvements in steam turbines and moreespecially to a segment of blades designed for insertior` in orattachment to the spindle or cylinder of a steam turbine, and which isto be produced as a finished article of manufacture capable ofwithstanding the severe vibration stresses to which it will be subjectedin the machine. y

rihe object of the invention is the production of a segment of bladesfor a turbine, which avoids the defects of the prior art structures,more especially being constructed to withstand vibration stresses.

yReferring to the drawings, Figure 1 is a plan view of a segment ofturbine blades, the shroud strip being partly broken away. Fig. 2 is anelevation of same. Fig. 3 is a sectional view of a portion of a segmentof blading, the section being taken in a plane of rotation. F ig. 4 is atransverse sectional view of same showing the detail of the 'securingmeans to the spindle or cylinder of the turbine.

in actual practice it has been found that a steam turbine constructedwith segments of blades calked in the spindle and cylinder,

and having shroud strips fastened to thel ends of the blades byriveting-over integral tenons formed on the ends of the blades andpreiiminarily inserted through holes punched therefor in the shroudstrips,-has not vbeen able to withstand vthe vibration stresses imposedon the built-up structure by reason of the high speeds at which theturbine was designed to run. The result was disastrous and the vbladesbecame detached.

As the result of an exhaustive study of the conditions entering into theconstruction and operation of such turbines, it has been found by actualtest that there'is a definite law controlling the the built-upstructures.

A segment of turbine blades made up with a Sankey foundation strip andwith a pitch of vibration of riveted shroud strip as hereinbeforereferred to, wasfastened securely in a vise at its foundation strip, avibratory tachometer was placed on the segment of blades so held andthesegment was then vibrated manually by quickly running a piece of hardmaterial over the blades in much the same manner asa bo would run astick along a picket fence. The tachometer gave a certain reading forthe pitch of the vibration thus produced, which reading it isunnecessary to state here in actual figures. A similar segment wasexperimented with in the saine way, except that the foundation strip wasycast-on to the ends of the blades, as a substitute for the Sankeyfoundation strip. When vibrated, the reading of the tachometer wassubstantially higher. Next, a

similar segment with the foundation strip cast-on was taken, but theshroud strip in this case, was soldered to the ends of the blades. Upontest, the tachometer again recorded a substantially higher figure asrepresenting the pitch of vibration. Lastly, a tie-strip was soldered atone side of the segment of blades, intermediate their ends, thefoundation strip being cast-on and the shroud strip being soldered on,and the tachorneter in this case again indicated a substantially higherfigure than before.

This investigation clearly indicated the theory upon which the presentinvention is based. It has been found, in one case, where the blades hadgone out on a turbine, where the shroud strip had been riveted on andwithout any tie-strip, that the vibration tachometer in a test ofsimilar seg- 'ments of blading to those used in that tur- Specifieationof Letters Patent. Pfgnted Jun@ 139 1915 bine, indicated substantiallythe same figure diderent mechanicalfastenings of the prior art. It isbelieved that the trailing ends of the shroud strips, if not thetrailing ends of the segment itself, whip during rotation,

I in much the same way as a flag whips in the wind. It was thereforefound that a stiff and rigid, but comparatively inelastic, trusslike -sement of blades is what is necessary to avoid this objectionablevibration and to raise the itch of vibration safely beyond the speed of)the turbine, so as not to be in resonance therewith. lt is found thatthe casting-in of the blades in the foundation strip, resulting in asoftening and annealing of the blade near the cast-on foundation strip,is an importantl factor toward arriving at the accomplishing of theobject of this invention. l Soldering a tie-strip to the blade at anintermediate point, and soldering a shroud strip at the end of theblade, are equally im ortant, factors for the attainment of thls result.Absence of any rojections whatever at the shroud strip asteningfsuch forinstance a-s the rivetedover tenon ends of the prior art, it is be'-lieved additionally prevents the tendency Ato set up objectionablevibration. Incidentally' it might be stated that in ,the prior artriveting-over ofthe tenon to fasten the shroud strip causes eitherlooseness, or distortion of the shroud strip itself, in Vthe case wherea blade happens to be slightly shorter than it ought to be; and thislooseness is, ofcourse, an element productive of vibration while' thedistortion of the shroud is objectionable for other reasons, primarilyfailure to baffle properly;` additionally, the rivet heads serve aspaddle brakes Vduring rotation.

It isunderstood that, in the prior art, a structure has been proposed towhich thin supporting strips have been welded to the blades and thenstout stiening rings have been soldered to the strips, or equivalentfastening means have'been used, but in all of these constructions thestout stifening ring is always present in addition to the 1t is as wellapplicable to a radial'low tur-l thin supporting strip. lf these wereused in an axial flow turbine with which the resent invention primarilydeals, although bine, it would be impossible -on account of the heavystructure to practicably baille the leakage ilowof steam around the endsof the blades of the segments, which the shroud strip in the` presentinvention is designed to accomplish. The weight of this heavy' structureis supported from the 'blades and this isobjectionable on account of theexcessive centrifugal force during rotation. It

should 'also be pointed out that those proposed constructions areprimarily applicable to gas turbines of the radial flow type. In such aturbine ,very high temperatures exist and soldering must be exceedinglyquestionable as a practicable fastening. Also in the prior art is to befound a turbine havinga few end blades of a segment brazed to a shroudstrip, but there the segment is mechanically fastened to the foundationstrip, and moreover thel shroudstrip is located adjacent the ends of theblades leaving projecting blade ends to objectionably serve as paddlesduring rotation. Also, it has been proposed to cast-0n both ffundationstrip and shroud strip, but in such construction the shroud strip wouldbe entirely too heavy to serve as a battle to prevent leakage of steamand its weight supported from the blades wouldlbe objectionable; itwould also be not uniform in texture if castV thin enough tobe apracticable baiiler.

Referring more particularly to the drawing, a series of blades l isshown cast-in in the foundation strip 2, and has fastened to its ends asingle, light shroud strip 4, by soldering the parts directly together.This mode of securing the shroud strip is preferable to welding as it isdifficult to prevent distortion of the partsin order to make a weld,Whereas such a high heat is not necessary in soldering. The solder 5 isclearly shown in Figs. 3 and 4. The klight shroud ing the tenon 6preferably With two parallel sides and two sides with a curvaturecorresponding to the surface of the blades. These tenons 6 are short,preferably only of sufcient length to fairly enter the holes punched inthe shroud strip 4. They. are shown of length equal to the thickness ofthe shroud strip 4 so as to be Hush with the surface of the shroud stripbetween the sides of the channel, which shape the shroud strip 4assumes. The object of extending the tenons` 6 into correspondinglyshaped holes in the shroud strip 4 is twofold, first, to properly spacethe blades, and second, to properly set the same at their theoreticalangle about their axes. The strip having been properly set againsttheextreme ends of the blades l, the same is soldered thereto preferablyby placing the-segment of blades in a position where the shroud strip 4is at the bottom; but, in the case of very small blades set closetogether, the segment lmay be so placed as to have the shroud strip 4 atthe top and thesolder 5 may be applied strong enough to rupture theblade itself I before pulling oil the shroud strip. After solderingtheshroud strip 4 tothe ends of blades 1, the structure' about thisfastening is then a smooth surface throughout the full extent of theshroud strip. This is important as presenting no paddle brake actionduring rotation.

A tie-strip 7 is soldered to the blades 1 at a point intermediatethereof, and preferably in notches provided in the blades. This featurealone, is not, of course, intended to be represented as novel. Thisstrip may be omitted in the case of short ilades or Where the speed iscomparatively The segment of blades as thus far con- 'structed, is thenmachined as ,to its foundation strip 2 and the shroud strip 4, so asfinally to produce an article of manufacture which is applicable to aturbine spindle or cylinder without any further machining. The finishedsegment is designed to be calked into a recess formed in the spindle orcylinder 3 of the steam turbine, as indicated in Fig. 4.

It should be understood that it is not desired to be limited to theexact details of construction shown and described, for obviousmodifications Will occur to a person skilled in the art.

It is claimed and desired to secure by Letters Patent,-

1. The combination of a plurality of blades, a cast-on foundation stripfor said blades, a single shroud strip soldered to the eXtreme ends ofsaid blades, a tie strip soldered to intermediate portions ofsaidblades, and means for fastening said foundation strip to a support.

2. The combination of a plurality of blades, a cast-on foundation stripfor said blades, a shroud strip soldered to the extreme ends of saidblades, a tie strip soldered to intermediate portions of said blades,and means for fastening said foundation strip to a support.

3. The combination of a plurality of blades, and a foundation strip, asingle light shroud strip, and a tie strip each united to said blades by`fusion of metal, and means 'for-fastening said foundation strip to aspindle or cylinder.

4. As an article of manufacture, la Segment of blading having afoundation strip, a single light shroud strip and a tie strip eachsecured to said blading by fusion of metal.

5. As an article of manufacture, a segment of blading having afoundation strip cast-on, a shroud strip soldered to the extreme ends ofsaid blading and a tie strip soldered to intermediate portions of saidblading. l 4

6. As an article of manufacture, a segment of'blading having afoundation strip, a single light shroud strip and a tie strip eachsecured to said blading by fusion of vmetal and said shroud strip beingsmooth throughout at its connection to said blading.

7. As an article of manufacture, a segment of blading having afoundation strip cast-on, a shroud strip soldered to the extreme ends ofsaid blading and a tie strip soldered to intermediate portions of saidblading, said shroud strip being smooth throughout at its connection tosaid blading.

8. As an article of manufacture, a seg-V ment of blading having afoundation strip and a previously formed single light rshroud strip eachsecured to said blading by fusion of metal and said shroud strip beingsmooth .throughout at its connection to said blading.

9. rlhe combination of a plurality of blades, a cast-on foundation stripfor said blades, a previously formed shroud strip soldered to theeXtreme ends of said blades, and means for fastening said foundationstrip to a support.

In testimony whereof, the signatures of the inventors are aliixed heretoin the presence of two Witnesses.

CHARLES EDWIN SEARCH. JOSEPH W. MOORE. Witnesses:

W. H. LmBER, Gr. F. DE WEIN.

